Rust 1.65 - let-else statements - new language feature!!! For youtube video: https://www.youtube.com/watch?v=U-5_bumwH9w&list=PL7r-PXl6ZPcCIOFaL7nVHXZvBmHNhrh_Q)

rust-let-else.rs

//! For youtube video: https://www.youtube.com/watch?v=U-5_bumwH9w&list=PL7r-PXl6ZPcCIOFaL7nVHXZvBmHNhrh_Q

/// Guard pattern with let-else
/// e.g., "my_key: 123"
pub fn key_num_guard_1(item: &str) -> Result<(&str, i32), &'static str> {
	let Some((key, val)) = item.split_once(':') else {
		return Err("Invalid item");
	};
	let Ok(val) = val.trim().parse::<i32>() else {
		return Err("Invalid item");
	};
	Ok((key, val))
}

/// Guard pattern with two guards, ok_or, and map_err
pub fn key_num_guard_2(item: &str) -> Result<(&str, i32), &'static str> {
	let (key, val) = item.split_once(':').ok_or("Item wrong format")?;
	let val = val
		.trim()
		.parse::<i32>()
		.map_err(|_| "Item value not i32")?;
	Ok((key, val))
}

/// Guard pattern with one final guard (ok_or)
pub fn key_num_guard_3(item: &str) -> Result<(&str, i32), &'static str> {
	let (key, val) = item
		.split_once(':')
		.and_then(|(key, val)| val.parse().ok().map(|val| (key, val)))
		.ok_or("Invalid item")?;

	Ok((key, val))
}

/// Nested if/else
/// e.g., "my_key: 123"
pub fn key_num_1(item: &str) -> Result<(&str, i32), &'static str> {
	if let Some((key, val)) = item.split_once(':') {
		if let Ok(val) = val.trim().parse::<i32>() {
			Ok((key, val))
		} else {
			Err("Invalid item")
		}
	} else {
		Err("Invalid item")
	}
}

/// Return early on Ok
/// e.g., "my_key: 123"
pub fn key_num_2(item: &str) -> Result<(&str, i32), &'static str> {
	if let Some((key, val)) = item.split_once(':') {
		if let Ok(val) = val.trim().parse::<i32>() {
			return Ok((key, val));
		}
	}
	Err("Invalid item")
}